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A microprocessor system
is pointless unless it
can communicate with the
outside world.
It does this through an
INTERFACE which is
usually a plug or
socket.
The CPU communicates
with this interface via
an INPUT/OUTPUT PORT
chip.
These chips are called
VERSATILE INTERFACE
ADAPTORS or UNIVERSAL
ASYNCHRONOUS
RECEIVER/TRANSMITTERS
etc.
Ports have their own
registers with
addresses, and the CPU
can write data to, or
read data from, these
registers.
If the system is
controlling a set of
traffic lights, then the
CPU can write data to
the registers, to switch
the lights in the
correct sequence.
It can also read data
that is provided to the
port by sensors buried
in the road.
This means that it can
make decisions according
to the amount of traffic
and switch the lights
accordingly.
Since the system is
digital and the outside
world is mostly
analogue, digital to
analogue converters are
required when providing
an output, such as one
to control the
temperature of an oven.
An analogue to digital
converter is required if
the system is to read an
analogue device, such as
a thermometer.
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